The present invention relates generally to gas turbine engines, and, more specifically, to industrial power generation gas turbine engines having low exhaust emissions.
An industrial power generation gas turbine engine typically includes a single rotor shaft joining a compressor to a turbine, with the turbine powering both the compressor and an external load typically in the form of an electrical generator. The engine is typically designed for efficient operation over a range of output power also known as load points. Most efficient operation is preferred at maximum rated power, or the base load, during which the engine is operated typically for a majority of its operating time. The full speed, no load condition allows the electrical generator to connect and disconnect from the electrical power grid. And, part load operating points exist therebetween.
Federal Environmental Protection Agency (EPA) regulations exist for ensuring that exhaust emissions from operation of the engine are below specified levels. Typical emissions include NOx, CO, and unburned hydrocarbons (UHC). Since turbines may be operated using either a gaseous fuel such as natural gas, or a liquid fuel such as No. 2 fuel oil separate emissions specifications have been promulgated due to the inherently different operation thereof. For example, natural gas is a much cleaner burning fuel and the low NOx limit specified therefor is 25 parts per million (ppm). Whereas, for liquid fuel, the low NOx limit is about 42 ppm, since liquid fuels do not burn as cleanly.
In order to achieve the low NOx level for liquid fuel, current gas turbine engines require the use of water injection either in its liquid or steam phase into the fuel and air mixture prior to undergoing combustion. Water injection accordingly increases the cost and complexity of the gas turbine engine.